Trouble in Iran. Israel's longstanding policy of "nuclear ambiguity" is based on strategic concerns, not legal obligations. It has not signed the Treaty on the Non-Proliferation of Nuclear Weapons, or NPT, so its assumed nuclear program doesn't violate any international agreements. An openly nuclear Israel, however, might give Iran, an original signatory, cover to withdraw from the treaty, since members may drop out if "extraordinary events … have jeopardized the supreme interests" of the country. It would also complicate the diplomatic efforts of the United States, which would surely be accused of hypocrisy for its hard line against Iran.

For most onlookers, any remaining doubts regarding Israel's nuclear status dissipated in 1986, when Israeli scientist Mordechai Vanunu gave photos and detailed accounts of the country's underground weapons factory to the SundayTimes. Based on Vanunu's information, scientists estimated that Israel had stockpiled between 100 and 200 nuclear weapons. (Israeli intelligence officers quickly seized and drugged Vanunu in Rome. He spent 18 years in an Israeli prison.) There have also been a number of verbal slips here and there. In a 2006 interview with a German television station, Israeli Prime Minister Ehud Olmert explicitly included his country in a list of nuclear states.

Israel wouldn't be the first non-NPT signatory to come out of the nuclear closet. India and Pakistan each tested a nuclear weapon only 15 days apart in 1998, suggesting that both countries had been harboring weapons of mass destruction for years. The United States and the G-8 nations imposed financial penalties against the South Asian rivals, but the G-8 lifted sanctions just a year later. The United States lifted its sanctions after Sept. 11, 2001. * There were no consequences at the U.N. level.

Even if Israel were an NPT signatory, it's unclear that acknowledging the nukes would trigger any serious penalties. The treaty does not include automatic sanctions for violators. Rather, a member state has to drag the miscreant country before the U.N. Security Council, where international alliances prevent swift action. Most experts agree that Iran has violated the NPT repeatedly. Sanctions, however, have been slow, sporadic, and relatively mild.

Explainer thanks Hans M. Kristensen of the Federation of American Scientists. Like Slate and the Explainer on Facebook. Follow us on Twitter.

Correction,May 26, 2010: This article originally stated that the United States' sanctions against India and Pakistan lasted until Sept. 11, 2001. The sanctions were lifted on Sept. 22, 2001, as a result of the Sept. 11 terrorist attacks. (Return to the corrected sentence.)

Correction, May 26, 2010: This article originally referred to Shimon Peres as the Israeli defense minister. He is the president of Israel but was defense minister at the time of the alleged attempted sale. (Return to the corrected sentence.)